package main

import (
	"encoding/hex"
	"fmt"
	"log"
	"time"

	"periph.io/x/conn/v3/gpio"
	"periph.io/x/conn/v3/gpio/gpioreg"
	"periph.io/x/conn/v3/spi"
	"periph.io/x/conn/v3/spi/spireg"
	"periph.io/x/devices/v3/mfrc522"
	"periph.io/x/devices/v3/mfrc522/commands"
	"periph.io/x/host/v3"
)

// mfrc522 rfid device
var rfid *mfrc522.Dev

// spi port
var port spi.PortCloser

// pins used for rest and irq
const (
	resetPin = "P1_22" // GPIO 25
	irqPin   = "P1_18" // GPIO 24
)

/*
Setup inits and starts hardware.
*/
func setup() {
	var err error

	// guarantees all drivers are loaded.
	if _, err = host.Init(); err != nil {
		log.Fatal(err)
	}

	// get the first available spi port eith empty string.
	port, err = spireg.Open("")
	if err != nil {
		log.Fatal(err)
	}

	// get GPIO rest pin from its name
	var gpioResetPin gpio.PinOut = gpioreg.ByName(resetPin)
	if gpioResetPin == nil {
		log.Fatalf("Failed to find %v", resetPin)
	}

	// get GPIO irq pin from its name
	var gpioIRQPin gpio.PinIn = gpioreg.ByName(irqPin)
	if gpioIRQPin == nil {
		log.Fatalf("Failed to find %v", irqPin)
	}

	rfid, err = mfrc522.NewSPI(port, gpioResetPin, gpioIRQPin, mfrc522.WithSync())
	if err != nil {
		log.Fatal(err)
	}

	// setting the antenna signal strength, signal strength from 0 to 7
	rfid.SetAntennaGain(5)

	fmt.Println("Started rfid reader.")
}

// close is idling the RFID device and closes spi port.
func close() {

	if err := rfid.Halt(); err != nil {
		log.Fatal(err)
	}

	if err := port.Close(); err != nil {
		log.Fatal(err)
	}

}

// stringIntoByte16 converst the given str into 16 bytes.
// String that are longer than 16 bytes, will be cut.
func stringIntoByte16(str string) [16]byte {
	var data [16]byte
	copy(data[:], str) // copy already checks length of str
	return data
}

// find first null byte
func clen(n []byte) int {
	for i := 0; i < len(n); i++ {
		if n[i] == 0 {
			return i
		}
	}
	return len(n)
}

// main starts setup, reads UID, write data tosector 2 block 0 and read writen data.
func main() {

	// init hardware
	setup()

	// trying to read UID
	data, err := rfid.ReadUID(5 * time.Second)
	if err != nil {
		log.Fatal(err)
	} else {
		fmt.Println(hex.EncodeToString(data))
	}

	// trying to write data
	err = rfid.WriteCard(5*time.Second, byte(commands.PICC_AUTHENT1B), 2, 0, stringIntoByte16("Hallo Welt"), mfrc522.DefaultKey)
	if err != nil {
		log.Fatal(err)
	} else {
		fmt.Println("Write successful")
	}

	// trying to read data
	data, err = rfid.ReadCard(5*time.Second, commands.PICC_AUTHENT1B, 2, 0, mfrc522.DefaultKey)
	if err != nil {
		log.Fatal(err)
	} else {
		str := string(data[:clen(data)])
		fmt.Println(str)
	}

	close()

}